Fear of huge asteroid impacts is a little similar to the fear of flying. The probability of anything happening is very small, but it's the vivid thought of such a catastrophic event happening that can make some of us magnify the probability in our minds leading us to have an irrational fear of such an event.
Thankfully, based on current calculations, the probability of a civilization-ending asteroid impact, like the one that killed off the dinosaurs 66 million years ago, is very low within our lifetimes. But how do we know this and what is the probability that we will see a large meteor impact?
What is the actual probability of a huge asteroid impact?
Space debris burns up in our atmosphere every day. Any space rock with a diameter of about 10-meters (33 feet), will be destroyed in the Earth's atmosphere during thermal explosions.
However, some of these space fragments do hit the ground. According to NASA, a meteor punched a hole in the rear end of an automobile in 1992, while a Connecticut dining room and an Alabama bedroom were also damaged by falling space debris in this century. And yet, there is no record of a human being having been killed by a small space rock in the last thousand years.
But what of the big ones? Some scientists claim we are overdue for an asteroid impact of the scale that took out the dinosaurs — as these happen approximately once every 50 to 60 million years.
The assertion, however, is highly debatable. First off, when we're talking in a scale of probabilities based on tens of millions of years, a tiny fraction in either direction is still a difference of hundreds of thousands, even millions, of years.
Secondly, the solar system is showing signs of relative tranquility. As the universe expands, stars move farther apart meaning fewer interactions between distant stars and space rocks, and less of a chance that a huge asteroid will have its trajectory altered to come hurtling in our direction.
According to NASA, the probability of an asteroid capable of destroying a city striking Earth is 0.1% every year. If one of these does hit Earth, there is a 70% chance it will land in the ocean, and a 25% chance it will land over a relatively unpopulated area. This is what happened with the Tunguska impact in Russia just over a hundred years ago.
The odds of a 5-10 kilometer wide asteroid, the likes of which made the dinosaurs go extinct, hitting Earth is almost negligible at 0.000001%.
Monitoring the skies
NASA's Near Earth Object program monitors space rocks in our neck of the universe. It has compiled a risk table for all known Near-Earth Objects (NEOs). For each of these, NASA calculates the likelihood of an impact with Earth for the next 100 years. The brains behind the operation? The calculations are made by Sentry, a highly automated collision monitoring computer system that scans the most up-to-date list of asteroids near Earth.
The Torino Scale, which runs from 1 to 10, is used to assess the danger we face from any individual asteroid. At the moment, nothing on the table is rated above 1 on the Torino Scale, meaning that impacts are calculated as being extremely unlikely.
What's more, as Wired points out, new private endeavors like the B612 Foundation are aiming to launch dedicated telescopes to analyze 90 percent of all asteroids that are more than 30-meters in diameter, as these are capable of leveling large areas.
As a reference, the meteor that impacted Chelyabinsk, Russia (video above) in 2013 causing millions of dollars of property damage and injuring over a thousand, was a relatively small meteor at 15 meters in diameter. Readings will become more and more accurate the more funds are invested in building monitoring systems.
Planetary defense is still important
All of this isn't to say that investment in planetary defense systems is not important. While NASA, and other organizations, are keeping an eye on the skies, asteroids are understandably difficult to spot.
In fact, just last year a large asteroid, called '2019 OK', was spotted just a day before flying between the Earth and the Moon. Even scarier than the size and proximity of the asteroid — it was the size of a football field and came within 65,000 km of Earth's surface — is the fact that it caught researchers off guard.
According to internal NASA documents obtained by Buzzfeed News, a NASA scientist said: "this one did sneak up on us."
If the asteroid had hit Earth, "the blast wave could have created localized devastation to an area roughly 50 miles across,” NASA said in a statement.
Worryingly, some researchers have claimed that planetary defense measures are underfunded. NASA chief Jim Bridenstine has said that we need to get serious about asteroid threats, while MIT planetary scientist Richard Binzel told BuzzFeed News that “it's no surprise an object like [2019 OK] would take us by surprise. Our current asteroid search capabilities are not up to the level they should be.”
While we have mentioned that we are living through a relatively calm period when it comes to asteroid impacts, there is still the occasional reminder that big impacts are still possible in our solar system.
For example, in 1992 a huge asteroid impact did occur and was observed on Jupiter. If the asteroid, called Shoemaker-Levy 9, had hit Earth, it would have created a global atmospheric disaster similar to the one that wiped out the dinosaurs 65 million years ago.
"Shoemaker-Levy 9 was a sort of punch in the gut," Heidi Hammel, who led the observations of the comet with NASA's Hubble Space Telescope, said in a NASA blog post.
"It really invigorated our understanding of how important it is to monitor our local neighborhood, and to understand what the potential is for impacts on Earth in the future."
Then there's 99942 Apophis, a huge asteroid that will fly so close to Earth in 2029 that our planet's gravitational pull will alter its trajectory.
What can we do if a large asteroid is headed our way?
As the European Space Agency, ESA, which is a part of the International Asteroid Warning Network, points out, there is a range of options available in the unlikely event that we do detect an asteroid on a collision course with Earth.
The most important factor would be how early the asteroid would be detected. While there is the very small, yet frightening, possibility that one could catch us unaware, like '2019 OK's' close flyby, which was spotted only 24 hours before occurring, current technology allows us to detect the trajectories of NEOs years in advance.
Options include reconnaissance missions in space to gather information, while nuclear impactors can also be used to try to break up or deflect the course of an asteroid into a safe trajectory. Preparations on the ground, meanwhile, would potentially involve evacuations of entire cities.
While asteroids might not be top of the priority list when it comes to threats towards civilization on Earth, it is still essential that we monitor space rocks and understand the way impacts could affect our planet in the future.